Unitel to renew H2S production

Unitel Technologies reports that is has been engaged by a Singapore company to review its plan for local decentralised production of hydrogen sulfide (H2S).

“Worldwide demand for H2S continues to grow. The use of H2S to make NaHS (commonly referred to as NASH) is an established market for mining and hydrometallurgy applications,” says Serge Randhava, CEO of Unitel. “Other uses have to do with the production of mercaptans and methionine, a valuable animal and poultry feed additive highly sought after in several Southeast Asian countries. Some emerging specialty H2S requirements are proprietary in nature.”

The basic question that Unitel has been invited to address by the client can be simply stated as follows. "Should pure sulfur feedstock react with hydrogen to make H2S, or does it make more sense to extract H2S from a refinery gas stream and purify it to a desired purity level of 99.5%?"

Capital and operating costs up to 30 tpd of H2S are fairly comparable for both options. However, when you go into the 50 - 200 tpd range, the sulfur/hydrogen reaction process offers some visible economic advantages. This is especially true if the H2S purification step requires removal of COS and/or CS2. It is relatively easy to separate hydrogen, nitrogen, methane and a majority of the water, but elimination of COS and CS2 needs an upstream hydrogenation reactor that requires an external supply of hydrogen.

The most significant advantage of the first option (making H2S by the direct reaction of molten sulfur with hydrogen) is that it offers a high level of flexibility. A well designed system can be tuned for a turndown ratio of 5 to 1. This means that H2S can be made on demand as and when its needed. This is important from a safety perspective because onsite storage of H2S can be minimised. On the other hand, long term contracts with H2S gas stream suppliers can be somewhat restrictive in nature.